1. Field of the Invention
The present invention relates to an electronic system which produces a trigger signal for activating a vehicle rider protection apparatus such as the airbag equipment at an event of collision of the vehicle
2. Description of the Prior Art
FIG. 1 is a block diagram showing, as an example, the conventional activation system of a vehicle rider protection apparatus disclosed in Japanese Patent Unexamined Publication No. 3-121951. In the figure, reference numeral 34 denotes an acceleration sensor which produces an electrical signal indicative of the acceleration of the vehicle, and 35 is a control circuit which activates the protection apparatus.
The control circuit 35 consists of an analog filter 35A for eliminating high-frequency noises, a sampling circuit 35B, an acceleration monitoring circuit 35C which detects the sampled acceleration signal reaching a certain level, and an arithmetic circuit 35D which converts the acceleration signal into a signal indicative of the change of vehicle speed and compares the resulting signal with the preset data. Indicated by 36 is a memory circuit, and 36A is a data table which is stored in the memory circuit 36 and used for the judgement of collision.
Next, the operation of this arrangement will be explained. At an event of collision of the vehicle, the acceleration sensor 34 produces an acceleration signal indicative of the acceleration caused by the collision, and sends it to the sampling circuit 36B through the analog filter 35A. The sampling circuit 36B samples the acceleration signal at a certain time interval, and delivers the signal to the arithmetic circuit 35D and acceleration monitoring circuit 35C.
The arithmetic circuit 35D integrates the acceleration signal thereby to evaluate the speed change, and it compares the calculated value with speed change data of collision which is stored as the collision judgement data table 36A in connection with the passing time after collision and the vehicle speed. If the arithmetic circuit 35D detects the calculated speed change in excess of the speed change data and, at the same time, if the acceleration monitoring circuit 35C detects the acceleration signal reaching the predetermined value, the arithmetic circuit 35D produces a trigger signal S for activating the vehicle rider protection apparatus.
The conventional activation system of vehicle rider protection apparatus is formed of a single circuit unit based on a microcomputer, for example, and therefore the protection apparatus will not be activated if the microcomputer fails, or the protection apparatus may be activated erroneously if the microcomputer mulfunctions, and the failure of the microcomputer in not indicated promptly to the vehicle rider.